The present invention relates to the manufacture of polyimide films, and more particularly to color polyimide films such as white polyimide.
Polyimide (PI) films are lightweight, flexible, and exhibit excellent mechanical properties as well as good resistance to heat and chemicals. Therefore, PI films are widely used in the electronics industry, such as in the fabrication of light-emitting diode (LED) devices, liquid crystal display devices, and the like. However, as the electronic industry advances, more demands are put on the quality and characteristics of PI films. In particular, certain design requirements may impose specific film coloration, e.g., opaque white, which is different from the conventional orange/yellow color characteristic of the PI film.
To form a white polyimide film, one known approach consists of coating a white resin (e.g., epoxy resin, acrylic resin or polydimethylsiloxane resin) on the conventional polyimide film for forming a dual-layered polyimide film. While this approach can form a polyimide film with the desired white tint, coating additional resin usually increases the manufacture cost and adversely affects film properties. In particular, because the resin coating generally has poor thermal resistance, color deterioration or yellowing can be usually observed when the PI film is exposed to thermal stress.
Another known approach consists of incorporating a white filler during the process of forming the polyimide film. In this manner, a polyimide film can be formed with the desired white color without the need of additional resin coating. This alternative approach typically adopts a “one-step method,” i.e., the condensation polymerization and ring-closing reaction of diamine monomers and dianhydride monomers are completed in one reactor, and a solution containing polyimide is directly obtained. The solvent of the polyimide solution can be then removed to obtain a solid polyimide film. Unfortunately, white polyimide films formed with this method still have insufficient resistance to chemicals and do not meet the design requirements for LED manufacture.
Therefore, there is a need for a white polyimide film that can have enhanced properties and can be manufactured in a cost-effective manner.